Sunday, August 29, 2010

Making an inlayed rosette, Part 2

Scraping is finished when the ends of each line appear square and the pattern looks okay. To ensure accuracy it works best to cut the rows into short lengths about 6" (150mm) long. These are easier to press together and the pattern stays more regular. I'll now repeat the gluing operation to make a little block from which I will saw tiles about 2mm (0.085") thick.

I made a rudimentary diagram showing the dimensions of the soundhole and the channel I'll need to rout for the inlay. This rosette will be about 5/8" wide, which will make for a dramatic statement. I decided to make it two-toned, black and red for visual interest. Each tile displays its own little variations. They definitely don't look machine made, and I like that. Why go to all the time and trouble to make this kind of thing when mass produced ones are available and cheap? I guess there are just some things we have to do that defy rational thinking and economics. Things that make life interesting.

Here's my template. This instrument will be similar in size to a Martin OM, just over 15" wide at the lower bout. I've chosen to include a Florentine style cutaway and that means I'll make some slight changes to some dimensions to make up for the loss of interior air volume this creates. I'll increase the body depth by 3/16" (4mm). I aim for a balanced output that couples power with lots of tone color.

The Sitka spruce top is one I got from David Freeman at Timeless Instruments. It has lots of character, with patches of bearclaw figuring. It's nice and stiff and even at this early stage it produces a complex set of sounds when I tap on it.

The template is 1/8" (3mm) hardboard and I've drilled positioning holes to poke a pencil through to mark brace locations and the cutaway. It's also wider than necessary to allow me to vary the width of the instrument by as much as 1/2".

My wife jokingly describes much of my working practice as, "getting jiggy with it". Now, -I actually use more hand tools and less machinery that a good many luthiers, but it's true. Guitar makers spend an inordinate number of hours creating devices designed to save a few minutes. Here's a $3 router compass made up from some hardboard, a wing nut and a dowel.

I hand planed the top just enough to clean up the surface. No matter how careful one attempts to be, it's easy to put scratches in with the router compass and inlay procedure. Also, the large volume of glue involved can cause the top to expand if it's too thin. To prevent any misalignment I went ahead and partially routed the soundhole. If I left it until afterwards, it's likely that the rosette would appear oval. Rout them at the same time and everything expands and contracts together. I didn't cut all the way through because I'll be hand planing the top to final thickness from the other side, and it's just easier if the hole isn't in the way.

The bordering lines are individual strips of veneer, 5 strips on each side. BBWBB The black strips are actually the result of a dying experiment gone slightly wrong. I didn't get complete penetration to the core so when they're planed down I end up with a complex grayish-black variegated appearance. The first time I used them I cursed, looked again and realized I really liked the effect!

Here's a little tip - by having the strips as individual lines rather than prelaminated, and not gluing them in place (they're dry at this stage, just held lightly in place with the pins), I've found I get a much tighter finished product. After the tiles are in place I'll wet the whole thing down really well with thinned glue. It seeps into the cracks, the lines all expand and everything sort of melts together.

The tiles as they are cut from the block are close to square in cross section. A slight angle is necessary to keep the pattern centered and prevent gaps. It's not necessary to belabor this! Just grab a wide chisel and do it by eye. Again, the slight variety is what makes the whole thing come alive! The regularity of machine precision ends up being visually static. Having the slight irregularity in the spacing and angle gives the characters a certain optical illusion. They seem to be moving across the colored background in a kind of dance.

I put a dab of glue on the bottom of the channel, and on the side of the adjoining tile before nestling things in place with the end of my brush. Any little spaces will magically disappear when the glue expands the veneer.

After brushing on a really thick coat of thinned glue (still using the yellow aliphatic), I let it dry thoroughly before planing things level. There's one little spot there on the treble side where the white line split and flaked off below the surface. I've been using some dyed white maple, but it's got some figure in it and tends to be a bit chippy. No problem. I'll just scarf in a little patch and it'll be invisible. The entire surface gets coated with thin superglue to seal off all that end grain even further and make it less likely to absorb dust or dirt in the interim before I apply the finish.

What does one do with the inevitable leftover tiles? You can pair them up with the scraps of ebony that every luthier can't bear to throw away. They make good tags to put on the key chains for a lockable guitar case. Or you could make jewellery for rebellious youth. A little time with the sandpaper and I came up with these vaguely plectrum-shaped forms.